Human influenza or “the flu” is a respiratory disease that is caused by influenza A and B viruses. Epidemics of influenza cause significant illness and death worldwide each year, and vaccination is the most straightforward strategy to prevent infection and disease. Traditional influenza vaccines expose the recipient to influenza virus proteins causing the recipient to mount an immune response to the proteins. Proteins (or polypeptides) used in vaccines are commonly called “antigens.” The commonly used seasonal influenza vaccines are based on the major antigen of the viruses, the hemagglutinin (HA). There are numerous influenza A subtypes having different HA antigens. Influenza A subtypes are divided and classified based on the HA and neuraminidase (NA) proteins that are expressed by the viruses. The influenza A subtype nomenclature is based on the HA subtype (of the sixteen different HA genes known in the art) and the NA subtype (of the nine different NA genes known in the art). Exemplary subtypes, include, but are not limited to, H5N1, H1N1 and H3N2. There are also variants of the influenza A subtypes which are referred to as “strains.” For example, the virus A/VietNam/1203/2004 is an influenza A virus, subtype H5N1, with a strain name A/VietNam/1203/2004.
Protection from the seasonal vaccines based on the HA is strain-specific and new strains emerge constantly, so the classical influenza vaccines have to be re-formulated each year in an attempt to match the currently circulating strains. See, Lambert and Fauci 2010. It is therefore highly desirable for next generation vaccines to be cross-protective and induce heterosubtypic immunity, i.e., vaccines against one subtype that protect or partially protect against challenge infection with influenza A of different subtypes.
The current ‘universal vaccines’ (i.e., vaccines designed to elicit heterosubtypic immunity) that are under development are mainly based on the more conserved internal influenza virus genes including the influenza matrix proteins (M1 and M2) (Schotsaert et al. 2009), the nucleoprotein (NP) and conserved parts of the HA (Bommakanti et al. 2010; Steel et al. 2010). The polymerase proteins PA, PB1 and PB2 also induce substantial T cell responses and may be also relevant targets (Assarsson et al. 2008; Greenbaum et al. 2009; Lee et al. 2008).
Next generation influenza vaccines currently under development include recombinant proteins, synthetic peptides, virus-like particles (VLPs), DNA-based vaccines and viral vector vaccines (Lambert and Fauci, supra). The advantage of using live viral vectors is their known property to induce high levels of cellular immunity, in particular CD8 T cells. Among the most promising viral vectors are vaccinia virus-based live vaccines (Rimmelzwaan and Sutter 2009) and adenovirus-based vectors (Hoelscher et al. 2006; Hoelscher et al. 2007; Price et al. 2010; Zhou et al. 2010). Single-dose mucosal immunization using an adenovirus construct expressing NP and M2, for instance, provided protection from virulent H5N1, H3N2 and H1N1 viruses (Price et al, supra). In a further study (Price et al. 2009), DNA vaccination with nucleoprotein (NP) and matrix 2 (M2) plasmids followed by boosting with antigen-matched recombinant adenovirus (rAd) provided robust protection against virulent H1N1 and H5N1 challenges in mice and ferrets.
Recombinant vaccines based on modified vaccinia virus Ankara (MVA) have been used in many non-clinical and clinical studies. MVA has proven to be exceptionally safe. No significant side effects have been obtained when MVA was administered to more than 120,000 human patients in the context of the smallpox eradication. Due to a block in virion morphogenesis the highly attenuated vaccinia virus strain fails to productively replicate in human and most other mammalian cells. Nevertheless, the ability to express viral and foreign genes in the early and late stage is retained. These characteristics make MVA a promising live vaccine vector that induces humoral and cellular immune responses and that exhibits a high safety profile.
U.S. Pat. Nos. 6,998,252; 7,015,024; 7,045,136 and 7,045,313 relate to recombinant poxviruses, such as vaccinia.
MVA-based vaccines have been used in clinical studies, for instance, against HIV, tuberculosis, malaria and cancer. In all of these studies, at least two doses were used. The human dose of an MVA-based vaccine was 5×107 to 5×108 PFU as applied in clinical trials (Brookes et al. 2008; Cebere et al. 2006; Tykodi and Thompson 2008;).
MVA has been used recently as a vector in pandemic H5N1 (Kreijtz et al. 2008; Kreijtz et al. PLoS One 2009; Kreijtz et al. Vaccine 2009; Kreijtz et al. J. Infect. Dis. 2009; Kreijtz et al. 2007; Mayrhofer et al., 2009; Poon et al. 2009) and H1N1 (Hessel et al. 2010; Kreijtz et al., J. Infect. Dis. 2009) influenza research. An MVA-based vaccine expressing NP and M1 is currently being tested in an ongoing clinical trial (Berthoud et al. 2011).
Thus, there remains a need in the art for a more broadly protective influenza vaccine.